The present invention relates to a vehicle occupant restraint system which is adapted to prevent a vehicle occupant from slipping forward under the seat belt in case of an impact situation such as a vehicle crash.
A seat belt is widely used for restraining a vehicle occupant to prevent the vehicle occupant from being thrown forward in case of an impact situation such as a vehicle crash, and hitting the instrumental panel or the steering wheel. An inflatable air bag is being used in an increasing number of vehicles to even further enhance the effectiveness of the seat belt. However, depending on the way the vehicle occupant is seated, the vehicle occupant could slip forward under the seat belt if the seat belt fails to restrain the pelvis of the vehicle occupant in an effective way. This is called xe2x80x9csubmariningxe2x80x9d, and substantially impairs the effectiveness of the seat belt.
It was therefore proposed to provide a moveable member inside the seat bottom so as to be deployed and restrain the thighs of the vehicle occupant in case of a vehicle crash. Such a thigh restraining member may be actuated typically by using a pyrotechnic actuator (see Japanese patent laid open publication No. 01-122504).
In such a vehicle occupant restraining device, typically, the front end of the seat bottom is raised so as to raise the knees of the vehicle occupant. This prevents the knees of the vehicle occupant from hitting the dashboard or other members opposing the vehicle occupant at the time of a vehicle crash, but the hip of the vehicle occupant inevitably slips forward to a certain extent and the reduction in the effectiveness of the vehicle seat belt due to the submarine phenomenon was not entirely avoided.
In view of minimizing the maximum value of the deceleration acting on the vehicle occupant at the time of a vehicle crash, it is desirable to transmit the deceleration to the vehicle occupant as soon as possible immediately following the occurrence of a vehicle crash. Because the integral value of the deceleration of the vehicle occupant from the occurrence of a vehicle crash to a complete stop is equal to the speed of the vehicle immediately preceding the vehicle crash, and is therefore fixed, any delay in the transmission of deceleration to the vehicle occupant needs to be made up for by a high level of deceleration in a later stage of the vehicle crash. In an actual vehicle crash, such a delay in the transmission of deceleration to the vehicle occupant is substantial because of the slack that may be present in the seat belt and the property of the seat belt to elongate when subjected to a tension.
On the other hand, if the restraining capability of the seat belt is simply increased by using a pretensioner device or other means for removing the slack and/or prohibiting the elongation of the seat belt, the upper part of the vehicle occupant such as the head and chest of the vehicle occupant are subjected to an excessive level of deceleration, and this is not desirable in view of minimizing the injury to the vehicle occupant.
In view of such problems of the prior art, a primary object of the present invention is to provide an anti-submarine vehicle occupant restraint system which can reduce the load on the chest and head of the vehicle occupant in an impact situation.
A second object of the present invention is to provide a vehicle occupant restraint system which can reliably prevent the submarining of the vehicle occupant at the time of a vehicle crash.
A third object of the present invention is to provide such a vehicle occupant restraint system which is simple in structure.
According to the present invention, such objects can be accomplished by providing a vehicle occupant restraint system for restraining a lower part of a vehicle occupant in a vehicle crash situation, comprising: a vehicle seat incorporated with a seat belt; a sensor for detecting an impact; a restraining member supported by a vehicle seat so as to be moveable from a retracted position concealed inside the seat to a deployed position projecting upward from the retracted position to restrain a forward movement of a hip area of the vehicle occupant; and a power actuator provided in association with the vehicle seat for actuating the restraining member to the deployed position according to a detection signal from the sensor; the power actuator being adapted to deploy the restraining member substantially before the seat belt effectively restrains the vehicle occupant.
Upon conducting extensive research, the inventors have discovered that the injury to the vehicle occupant is often caused by a high level of acceleration that is applied to the vulnerable part of the vehicle occupant such as the chest and head, and that the mechanical strength of the waist of a vehicle occupant is high enough to withstand the forward force at the time of an impact with a certain margin. It was therefore concluded that the injury to the vehicle occupant can be minimized by appropriately selecting the force and timing of restraining the pelvis and the adjacent parts (such as thighs and hip) relative to the timing of the seat belt restraining the chest area of the vehicle occupant.
Because the load acting on the vehicle occupant is thereby more distributed, the maximum load on the critical parts of the human body such as the chest and head can be reduced. In particular, the pelvis or waist and the parts adjacent thereto have a relatively high mechanical strength as compared to other parts of the human bone structure, and are relatively free from load at the time of an impact if the vehicle occupant is seated so that an early increase in the load on this part would not create any significant problem.
Preferably, a vertical height of the restraining member at the deployed position is equal to or higher than an ischium of the vehicle occupant seated in the seat. Thereby, the forward movement of the hip of the vehicle occupant can be effectively restrained, and the desired timing for restraining the hip of the vehicle occupant can be achieved.
According to a preferred embodiment of the present invention, a vertical height of the restraining member at the deployed position is at least 20 mm higher than an ischium of the vehicle occupant seated in the seat, and projects 20 mm or less into the part of the thighs of the vehicle occupant immediately above the restraining member at the deployed position.
It was also found to be desirable to restrain a part of the thighs of the vehicle occupant which is relatively close to the pelvis or more particularly the ischium of the vehicle occupant. According to a preferred embodiment based upon such a recognition, the restraining member at the deployed position is higher than an ischium of the vehicle occupant seated in the seat, and is 80 mm to 220 mm ahead of the ischium of the vehicle occupant.
The power actuator can be made highly compact when it consists of a pyrotechnic power actuator comprising a cylinder, a piston received therein, and a propellant received in the cylinder for rapidly increasing an inner pressure of the cylinder so as to produce a thrust that will rapidly push the piston out of the cylinder. To evenly apply a restraining force to the thighs of the vehicle occupant, and ensure a necessary mechanical strength without requiring any massive components, the restraining member may comprise a laterally extending main member supported by free ends of a pair of arms having base ends pivotally supported by a seat frame.
Typically, the pivotally supported base end of each arm is located behind the main part of the restraining member, and the power actuator is located behind of the main part of the restraining member.
Because the restraining member is desired to continue to apply a restraining force to the vehicle occupant for a certain period of time following a vehicle crash, it is desirable to provide a one-way lock mechanism in the power actuator or other parts of the restraint system for substantially preventing a reversing movement of the restraining member once it is deployed.
The orientation of the arm can be reversed, and by so doing, it is possible to retain the restraining member at its deployed position once it is deployed without requiring any special arrangement because the inertia acting on the vehicle occupant urges the restraining member toward its deployed position as long as it exists.